Fix doc links (#14650)

* Update freebsd.md

* Update REFERENCE.md

* Update README.md

* Update COLLECTORS.md

collectors/COLLECTORS.md

@@ -274,7 +274,7 @@ configure any of these collectors according to your setup and infrastructure.
 - [NSD](https://github.com/netdata/netdata/blob/master/collectors/python.d.plugin/nsd/README.md): Monitor nameserver
   performance metrics using the `nsd-control`
   tool.
-- [NTP daemon](https://learn.netdata.cloud/docs/agent/collectors/go.d.plugin/modules/ntpd): Monitor the system variables
+- [NTP daemon](https://github.com/netdata/go.d.plugin/blob/master/modules/ntpd/README.md): Monitor the system variables
   of the local `ntpd` daemon (optionally including variables of the polled peers) using the NTP Control Message Protocol
   via a UDP socket.
 - [OpenSIPS](https://github.com/netdata/netdata/blob/master/collectors/charts.d.plugin/opensips/README.md): Collect

collectors/charts.d.plugin/sensors/README.md

@@ -10,7 +10,7 @@ learn_rel_path: "Integrations/Monitor/Devices"
 # Linux machine sensors monitoring with Netdata
 
 Use this collector when `lm-sensors` doesn't work on your device (e.g. for RPi temperatures). 
-For all other cases use the [Python collector](/collectors/python.d.plugin/sensors), which supports multiple 
+For all other cases use the [Python collector](https://github.com/netdata/netdata/blob/master/collectors/python.d.plugin/sensors), which supports multiple 
 jobs, is more efficient and performs calculations on top of the kernel provided values.
 
 This plugin will provide charts for all configured system sensors, by reading sensors directly from the kernel.

health/REFERENCE.md

@@ -741,7 +741,7 @@ info: average ratio of HTTP responses with unexpected status over the last 5 min
 
 ## Expressions
 
-Netdata has an internal [infix expression parser](/libnetdata/eval). This parses expressions and creates an internal
+Netdata has an internal infix expression parser under `libnetdata/eval`. This parses expressions and creates an internal
 structure that allows fast execution of them.
 
 These operators are supported `+`, `-`, `*`, `/`, `<`, `==`, `<=`, `<>`, `!=`, `>`, `>=`, `&&`, `||`, `!`, `AND`, `OR`, `NOT`.

packaging/installer/methods/freebsd.md

@@ -113,7 +113,7 @@ The following options are mutually exclusive and specifiy special operations oth
 - `--uninstall`: Uninstall an existing installation of Netdata. Fails if there is no existing install.
 - `--claim-only`: If there is an existing install, only try to claim it without attempting to update it. If there is no existing install, install and claim Netdata normally.
 - `--repositories-only`: Only install repository configuration packages instead of doing a full install of Netdata. Automatically sets --native-only.
-- `--prepare-offline-install-source`: Instead of insallling the agent, prepare a directory that can be used to install on another system without needing to download anything. See our [offline installation documentation](/packaging/installer/methods/offline.md) for more info.
+- `--prepare-offline-install-source`: Instead of insallling the agent, prepare a directory that can be used to install on another system without needing to download anything. See our [offline installation documentation](https://github.com/netdata/netdata/blob/master/packaging/installer/methods/offline.md) for more info.
 
 Additionally, the following environment variables may be used to further customize how the script runs (most users
 should not need to use special values for any of these):